GB2194579A

GB2194579A - Door seal

Info

Publication number: GB2194579A
Application number: GB08621032A
Authority: GB
Inventors: William Iain Mackie Henderson; David John Morrison; Moira Smith; David John Thornley; Samuel Hall Leask; Christopher F Matthews
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1986-08-30
Filing date: 1986-08-30
Publication date: 1988-03-09
Also published as: GB2194579B; GB8621032D0

Abstract

A seal to avoid penetration of electromagnetic interference comprises a tortuous path of interfitting grooves and ridges on the door and frame and in which rubber seals 28 covered with a metal braid 19A fit into the base of the grooves and are compressed, when the door is closed. The faces 18,19 of this ridge converge less rapidly towards its end than elsewhere i.e. towards point P1 rather than point P2. This causes a wiping action of the ridge against the braid serving to remove oxidation and ensuring a good electrical contact. <IMAGE>

Description

SPECIFICATION Electromagnetic sealing arrangement for a door assembly This invention relates to a door assembly designed to avoid penetration by electromagnetic interference. It arose in the design of a container or shelter for transportable electrical equipment.

In a known arrangement a ridge extends around a rim of the door and fits into a groove extending around the door surround. A solid resiliently compressible insert of electrically conductive material is set at the bottom of the groove and engages the ridge so as to form an electromagnetic seal. Whilst this arrangement does work to a certain extent the seal is not perfect and tests have shown that an oxide film can form on the co-operating surfaces making an imperfect electrical connection.

This invention provides a door assembly comprising a door rim and a door surround, one having a ridge extending around it and the other having a groove extending around it and arranged to receive the ridge when the door is closed; the groove having inclined faces which converge towards its base and receiving at its base, a resiliently compressible conductive seal and the ridge having correspondingly inclined faces which converge towards its tip more tapidly in a region close to the tip than in regions farther from the tip.

By employing the invention it has been found that the problem of oxidation and bad contact is overcome and that the conductive seal is rubbed or wiped by the free end of the ridge each time the door is opened and closed so as to remove any oxidation.

The base of the groove is preferably enlarged to form a socket which receives the seal. The latter is preferably a tube of rubber or synthetic rubber and it can have a circular cross-section to fit into a corresponding circular socket. The tube may be rendered conductive by being covered with a metal braid.

Another possibility would be to use conductive rubber.

The relative arrangement of the ridge and groove is preferably such that the tip of the groove enters the aforementioned socket when the door is closed and the seal is compressed.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a horizontal cross section through a door and door frame forming part of a shelter for electronic equipment and constructed in accordance with the invention; and Fig. 2 is a detailed view of a flexible seal and associated parts also shown in less detail in figure 1.

The illustrated door assembly comprises a door-frame formed from four lengths of extruded aluminium, all having the same cross section. Only the upright lengths 1 and 2 are illustrated and these are attached to wall panels 3 whose edges are received in channels defined between flange 1A and securing strip 4 on the right hand side of figure 1; and between flange 2A and securing strip 4 on the left hand side of figure 1.

The door-frame receives a door formed by a rim and a door panel. The door-rim is formed from four lengths of extruded aluminium, all having the same cross sectional shape. Only the upright lengths 5 and 6 of the door-rim are illustrated. As can be seen from figure 1, these define channels into which the door panel 7 fits.

The door is hinged to the frame, about an axis 8, by a hinge 9 which is displaced to one side of a plane 10 passing centrally through the door panel 7.

The door-rim upright 5 defines three "first" faces 11,12,13 directed away from the hinge and four "second" faces 14,15,16,17 directed towards the hinge. These co-operate with "second" faces 18,19,20 and "first" faces 21,22,23,24 respectively on the doorframe upright 1 to define a tortuous path between door and frame. This attenuates RF energy which might otherwise leak pass abutting faces 25 and 26 when the door is closed, Seals 27,28,29 are located on cylindrical sockets 30 defined between faces 18,21; 11,15 and 19,22. Seal 27 is made of rubber tubing and provides weather proofing. Seals 28 and 29 are of similar construction but are covered in conductive braid 31 (Fig 2). The conductive braid 31 provides the necessary electrical connection between the door-rim and the door-frame to provide a seal against electromagnetic interference.

There are thus three features by which the seal against electromagnetic interference is produced: 1. the abutting faces 24 and 25; 2. the braid covered rubber seals 28 and 29; and 3. the tortuous passage between door rim and door frame.

The axis 8 about which the door hinges is displaced from the centre plane 10 and this displacement causes movement of the faces 11, 12, 13 as the door opens to have a component parallel to the plane 10 during a period before the noses on the door clear the noses on the frame. This imposes a limitation on the steepness of the slope of the faces 11,12 and 13 permissable without causing them to foul against corresponding faces 18,19 and 20.

Because the "first" faces 11,12 and 13 are progressively more distant from the axis 8 of the hinge, the displacement from the centre plane of the door is progressively less signifi cant and the movement has a progressively smaller component in the direction of the centre plane 10. Thus the "first" faces 11,12 and 13 can be made progressively steeper and define angles A1,A2,A3 with the centre plane 10 as illustrated in figure 1. The displacement of the hinge causes the "second" faces 14,15,16 and 17 of the door to tend to move away from their opposing "first" faces 21 22,23 and 24 of the door frame so that they can be made relatively steep and, as can be seen from the drawing, they each define an angle at least as great as A3.

The upright 6 remote from the hinge is formed from the same extrusion dye as that from which the upright 5 is made and has an identical cross section. The faces on the upright 6 are denoted by reference numerals identical to those used for corresponding faces of the upright 5 but with addition of the suffix letter A. It will be noted from the drawing that the relatively steep faces 14A,15A,16A and 17A face away from the hinge axis 8 and that this is appropriate since their distance from the hinge is sufficient to make a steep angle permissable without risk of fouling on the corresponding faces of the door frame member 2 (which is identical to the frame member 1).

By use of the increasing angles A1,A2,A3 and of the even greater angles A4 AS A6; the maximum length and tortuousness of the passage is obtained; and the maximum number of angled lengths of the tortuous passage can be fitted into the width W1 of the extruded members 2 and into the width W2 of the extruded member 6. This in turn allows up to four RF seals to be used (although only two are employed in the illustrated embodiment) whilst still leaving space for a weather seal 27. This latter feature is important since it avoids the need for a separate seal around an edge such as that shown at 32 of the frame as has previously been needed.

It was found during initial environmental tests that oxidation of the metal braid 31 could cause an imperfect electrical contact.

This difficulty was overcome by shaping the noses 32 (defined between faces 18,19 and 12,15) in a manner as is apparent from figure 2; from which it can be seen that the inclined faces 18,19 have portions 18A,19A in an end region d2 of the nose which converge towards a point P1 less rapidly with respect to distance d along the nose than in a major region dl, where they converge towards a point P2.-The extreme end#of the nose, in region d3, is rounded with a circular form centred at point P3.

From figure 2 it can be seen that the region d2 of each nose enters a cylindrical socket 30 in which the corresponding seal is located so that, when the door is closed, the tip of the nose coincides with the axis of the cylindrical shape of the socket. During movement of the nose to and from the closed position it has been found that a rubbing action occurs between the metal braid 31 and the nose, this serving to wipe away any oxide film which may have formed on the co-operating surfaces. This self-cleaning action is a feature claimed in our co-pending patent application of even date.

Claims

1. A door assembly comprising a door rim and a door surround, one having a ridge extending around it and the other having a groove extending around it and arranged to receive the ridge when the door is closed; the groove having inclined faces which converge towards its base and receiving, at its base, a resiliently compressible conductive seal; and the ridge having correspondingly inclined faces which converge towards its tip more rapidly in a region close to the tip than in regions farther from the tip.

2. A door assembly according to claim 1 in which the base of the groove is enlarged to form a socket revealing the seal.

3. A door assembly according to claim 1 or 2 in which the seal is a tube of rubber or synthetic rubber.

4. A door assembly according to claim 3 in which the tube has an outer covering of metal braid.

5. A door assembly according to claim 2 in which the tip of the ridge enters the socket when the door is closed.

6. A door assembly having a sealing ararrangement substantially as described with reference to figure 2 of the accompanying drawings and substantially as illustrated therein.